In the present description, for clarity and where appropriate, double layer capacitors (DLCs) are referred to as non-hybrid DLCs or hybrid DLCs.
A typical non-hybrid DLC consists of two high surface area electrodes (typically activated charcoal electrodes) immersed in an electrolyte such as an acid or other electrolyte. The electrolytes are typically aqueous, but may be non-aqueous. The two high surface electrodes are separated by an extremely thin and porous separator. On charge ions are adsorbed onto the high surface area electrodes, anions on the positive electrode and cations onto the negative electrode. On discharge the ions desorb from the electrodes. A typical acid type DLC provides close to one million charge/discharge cycles and stores about 1.5 Wh per kg of DLC.
In order to increase the energy stored in a DLC, hybrid systems, having the characteristics of a capacitor and the characteristics of a rechargeable battery, have been developed. For example, U.S. Patent Application 2008/0199737 to Kazaryan et al., whose disclosure is incorporated herein by reference, describes a hybrid lead-acid battery/electrochemical capacitor electrical energy storage device.
Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.